1. Field of the Invention
The present invention relates to recording media reproducing apparatus. More particularly, the present invention relates to a reproducing apparatus for recording media on which digital data in a plurality of channels are recorded.
2. Description of the Related Art
CD (compact disc) players are known as reproducing apparatus capable of reproducing music data and the like from an optical disc. There have been also proposed reproducing apparatuses utilizing a data-rewritable magneto-optical disc on which a user can record music data and the like.
In some reproducing apparatuses utilizing such disc media, the vibration-resisting function has been improved by the use of a buffer memory.
Specifically, during reproduction by such a reproducing apparatus, audio data read out from a disc are intermittently written in a buffer memory at a high transfer rate and are continuously read out from the buffer memory at a low transfer rate to be demodulated as audio reproduction signals. At this time, the buffer memory always keeps some data accumulated therein. Therefore, even if an external vibration or the like causes a track jump leading to a temporary interruption in the data readout from the disc, data can be continuously read out from the buffer memory. This allows the reproduction sounds from the reproducing apparatus to be output without interruption.
An example of a recording format used in such a reproducing apparatus will now be described with reference to the drawings.
As shown in FIG. 1A and FIG. 1B, a recording track on a magneto-optical disc has continuous clusters CL (=36 sectors) each including a subdata area having four sectors (one sector=2352 bytes) and a main data area having 32 sectors (SC0-SC30), one cluster constituting the minimum unit for recording. Such a cluster corresponds to two or three turns along the track. An address is recorded for each sector.
The subdata area consisting of four sectors is used for subdata or as a linking area and the like while TOC data, audio data and the like are recorded on the main data area consisting of 32 sectors.
A music data area recorded in a sector is subdivided into sound groups, and eleven sound groups constitute two sectors.
Specifically, the even sectors in FIG. 1B (SC0, SC2, SC4, etc.) are configured as shown in FIG. 1C while the odd sectors in FIG. 1B (SC1, SC3, SC5, etc.) are configured as shown in FIG. 1D.
As shown in FIGS. 1C and 1D, each sector has a header in which a synchronization pattern SYNC and an address AD are recorded at the beginning thereof followed by a subheader, and actual audio data are recorded following the subheader.
A sound frame SF containing 212 bytes constitutes the minimum data unit for recorded audio data, and eleven sound frames are included in every two sectors. One sound frame is data which are obtained by compressing audio signals for 11 msec in an L- or R-channel.
In an even sector, recording is performed alternately in the L- and R-channels, i.e., the recording is performed in a sound frame SF.sub.(L0) of the L-channel, a sound frame SF.sub.(R0) of the R-channel, a sound frame SF.sub.(L1) of the L-channel and so on up to a sound frame SF.sub.(L5) of the L-channel.
On the other hand, the alternate recording continues in an odd sector, i.e., the recording is performed in a sound frame SF.sub.(R5) of the R-channel, a sound frame SF.sub.(L6) of the L-channel, a sound frame SF.sub.(L6) of the R-channel and so on up to a sound frame SF.sub.(R10) of the R-channel.
A pair of sound frames of the L- and R-channels constitute one sound group (SG0-SG10). Therefore, the sound groups SG0-SG4 and the first half of the sound group SG5 are recorded in the even sector while the second half of the SG5 and the subsequent sound groups up to SG10 are recorded in the odd sector. Thus, the data for the eleven sound groups are recorded in the two sectors as described above.
When data recorded on a disc in such a format are recorded and reproduced through the buffer memory, the buffer memory performs storage on a sector basis. Specifically, access addresses are generated by combining the addresses of sectors and the byte addresses in the sectors (0-2351 bytes) to allow data writing and reading.
Data temporarily stored in the buffer memory are read out again on a sector basis to be supplied to a decoder provided downstream thereof which performs, for example, a process of decoding the audio-compressed data to obtain output as reproduction signals in two channels, i.e., L- and R-channels. As apparent from the above-described sector format, transfer of the data in an even sector to the decoder is sequentially performed starting with data in the L-channel (i.e., sound frame SF.sub.(L0)) while transfer of the data in an odd sector to the decoder is sequentially performed starting with data in the R-channel (i.e., sound frame SF.sub.(R5)). In other words, the data transfers for the L- and R-channels take place in reverse ways between an even sector and an odd sector.
When each sector is written in and read out from the buffer memory in the correct order and the read data are transferred to the decoder, the transfers of data in L- and R-channels alternately take place without fail when viewed on a sound frame basis, which creates no problem. Specifically, the decoder performs a decoding process for each of the sound frames thus fetched to expand the compressed data to obtain audio data for 11.6 msec and outputs the data alternately as L-channel data and R-channel data. Therefore, if the sound frames of the L- and R-channels are properly alternately supplied, the sound frames of the L- and R-channels can be directly output as audio data in the L- and R-channels, respectively.
However, in the event that transfer of the data in an even sector is followed by transfer of the data in another even sector due to an error during fetch or readout of sector data at the buffer memory or an error in the transfer process, a transfer error occurs, wherein data in the L-channel are consecutively transferred.
If the alternate transfer of sound frames in the L- and R-channels can not be maintained any more in such a situation, the decoder will output decode data on the data of the sound frames in the L-channel as audio data in the R-channel and will output decode data on the data of the sound frames in the R-channel as audio data in the L-channel conversely.
Thus, reversal of L- and R-phases occurs in the reproduced sound, which causes the so-called phase shifts in stereo sounds.